Conventionally, touch panels for use in electronic notepads and personal computer include those of analog resistive-film type. Generally, as shown in FIG. 9, a lower-side electrode member 402 having: a transparent electrode 422 on a part of the top face of a transparent insulating base member 421; a pair of bus bars 423, 424 disposed on two parallel sides of the transparent electrode 422; and routing circuits 425, 426 disposed on a portion other than the transparent electrode 422, for connecting the bus bars 423, 424 and external terminals, and an upper-side electrode member 401 having: a transparent electrode 412 on a part of the bottom face of a transparent insulating base member 411 having flexibility; a pair of bus bars 413, 414 disposed on two parallel sides of the transparent electrode 412; and routing circuits 415, 416 disposed on portions other than the transparent electrode 412, for connecting the bus bars 413, 414 and external terminals, are disposed facing each other via an insulative spacer 403 in such a way that the bus bars 413, 414, 423, 424 are arranged in a square pattern, and their peripheral portions are bonded to each other. Moreover, the other ends of the routing circuits 415, 416, 425, 426 are arranged to be on one side of the touch panel and are connected to the end portions of film connectors 407.
The principle of the analog resistive-film type transparent touch panel is such that as shown in FIG. 10, when an arbitrary point P is pressed from the top of the upper-side electrode member 401 by fingers and pens to establish a point-contact between the portions of points P of both the transparent electrodes 412 and 422, a voltage is applied to the transparent electrode 412 of the upper-side electrode member 401 while no voltage is applied to the transparent electrode 422 of the lower-side electrode member 402 so that a potential gradient is generated in the X direction on the transparent electrode 412 of the upper-side electrode member 401 while a divided voltage ex is generated at the point P on the transparent electrode 412 of the upper-side electrode member 401 and the voltage ex is detected from a divided voltage output terminal 405 of the lower-side electrode member 402. Herein, when a coordinate of the point P is (x, y), a distance between the bus bars 413 and 414 of the transparent electrode 412 in the upper-side electrode member 401 is L1, and a voltage between the bus bars 413 and 414 is E, the relation of ex/E=x/L1 is established, which makes it possible to obtain the x-coordinate of the point P from the voltage ex. Moreover, in the case where a voltage is applied to the transparent electrode 422 of the lower-side electrode member 402 while no voltage is applied to the transparent electrode 412 of the upper-side electrode member 401, a divided voltage ey is generated at the point P on the transparent electrode 422 of the lower-side electrode member 402 and the voltage ey is detected from a divided voltage output terminal 404 of the lower-side electrode member 401. Herein, when a distance between the bus bars 423 and 424 of the transparent electrode 422 in the lower-side electrode member 401 is L2, and a voltage between the bus bars 433 and 434 is E, the relation of ey/E=y/L2 is established, which makes it possible to obtain the y-coordinate of the point P from the voltage ey.
Recently, as products becomes smaller in size and screens becomes larger in size, it is desired to form these touch panels such that the bus bars and the interconnections of the routing circuits are fitted in the range of a thin frame which is a slim region starting from the edge of the panel.
However, since the bus bars 413, 414, 423, 424 and the routing circuits 415, 416, 425, 426 are produced from such materials as a conductive paste made by dispersing conductive fillers such as metals including gold, silver, copper, and nickel; and carbons in resin binders, there are the following issues. The interconnections of the bus bars 413, 414, 423, 424 and the routing circuits 415, 416, 425, 426 gain a resistance larger than a specific resistance of the conductive fillers due to the resin which is contained therein as a binder. While a touch position when a constant voltage is applied to the touch panel is determined by the voltage ex in the X direction and the voltage ey in the Y direction detected at the divided voltage output terminals as described above, if there is a resistance in the bus bars 413, 414, 423, 424 even with the x-coordinate of the touch position being identical, the x-coordinate of the detected position does not completely coincide at a section close to the connection portion to the routing circuits 415, 416, 425, 426 (a in FIG. 9) and at a section away from the section (b in FIG. 9). The same applies to the case where the y-coordinate of the touch position is identical. The bus bars 413, 414, 423, 424 have a large resistance as they are formed from a conductive paste material, and the resistance is further increase as the bus bars 413, 414, 423, 424 are formed to be thinner, which emphasizes a difference between position detection at the section close to the connection portion to the routing circuits 415, 416, 425, 426 (a in FIG. 9) and position detection at the section away from the section (b in FIG. 9). More particularly, due to linearity, movements by fingers or pens on the transparent touch panel cannot be inputted as they are, resulting in difference in input data. Forming the bus bars 413, 414, 423, 424 to be thicker makes the difference of position detection less prominent, though it hinders achievement of the thin-frame touch panel.
In the touch panel, a specified correction (calibration) is performed so as to see the touch panel in such a manner that the touch position of the touch panel and a displayed position on an LCD obtained through detection of the touch position can be overlapped with respect to each other. While the touch position when a constant voltage is applied to the touch panel is determined by the voltage ex in the X direction and the voltage ey in the Y direction detected at the divided voltage output terminals as described above, a detected voltage changes when a resistance of the transparent electrode is changed with time or changed with ambient temperature, resulting in displacement from the displayed position on the LCD. The bus bars and the routing circuits have a large resistance as they are structured from a conductive paste material, and with larger interconnection resistance, the degree of displacement when the transparent electrode is changed with time or with ambient temperature increases. As described above, division of a constant voltage E leads to determination of the input position, though more precisely, the constant voltage E includes an interconnection resistance and so it becomes a voltage E′ in the bus bars, whereby division of the voltage E′ leads to determination of the input position.
Consequently, in the case where the interconnection resistance does not change with time or with ambient temperature but the resistance of the transparent electrode changes with time or with ambient temperature, the more the interconnection resistance increases, and the larger the change of E′ due to the change with time or the change with ambient temperature becomes, which emphasizes the displacement between the touch position on the touch panel and the displayed position on the LCD. By forming the bus bars and the routing circuits to be thicker, the displacement between the touch position on the touch panel and the displayed position on the LCD, if occurring, is made less prominent, though it still hinders achievement of the thin-frame touch panel.
As described above, the conventional touch panel has a limit in pursuit of the thin-frame configuration, and in the case of large-size touch panels, the bus bars and the routing circuits are lengthened, which increases the interconnection resistance, resulting in further difficulty in achievement of the thin-frame touch panel.
Accordingly, in order to solve these issues, the inventors of the present invention have proposed to form the bus bars and the routing circuit interconnections with use of only metal materials as their component materials (see Japanese Unexamined Patent Publication No. 2001-216090 A). More specifically, they are made of metal materials composed only of gold, silver, copper, nickel, or the like formed by an electroplating method, vacuum evaporation method, sputtering method, ion plating method, CVD method, or the like.
However, the bus bars and the routing circuits disclosed in Japanese Unexamined Patent Publication No. 2001-216090 A had the following issues.
First, the bus bars and the routing circuits formed with the use of only metal materials as their component materials in Japanese Unexamined Patent Publication No. 2001-216090 A are formed by the electroplating method, vacuum evaporation method, sputtering method, ion plating method, CVD method, or the like. Since these methods except the electroplating method are formation means in which after a metal thin film is formed on the entire surface, unnecessary portions for the bus bars and the routing circuits need to be removed, the removed metal materials are wasted, thereby causing such an issue that the manufacturing cost of the touch panel is high. Moreover, in the electroplating method, the entire surface is immersed in a plating bath, and so even if rinsing is applied afterward, the transparent input region may be polluted, causing an issue of yields.
Moreover, since the bus bars and the routing circuits are thin films formed by the electroplating method, vacuum evaporation method, sputtering method, ion plating method, CVD method, or the like, the size of their cross sectional areas are largely influenced by the formation widths of the bus bars and the routing circuits. Consequently, if the thin-frame configuration is implemented, the cross sectional areas of the bus bars and the routing circuits decrease, i.e., the resistance increases, by which errors in position detection on the touch panel occur more easily. While forming the bus bars and the routing circuits to be thicker makes the difference in position detection less prominent, forming a film to have a thickness of 30 μm or more by the above-described film formation methods takes an extremely long time, thereby causing an issue of deteriorated production efficiency. Moreover, in the methods other than electroplating method, including the vacuum evaporation method, sputtering method, ion plating method, and CVD method, forming the film to have a larger thickness proportionally increases the metal materials to be removed, thereby further aggravating the issue of cost.
Therefore, an object of the present invention is to solve the aforementioned issues and to provide a thin-frame touch panel which is inexpensive, free from errors in position detection, and sufficient in yields and efficiency during production.